1. Field of the Invention
The present invention relates to a donor substrate for a flat panel display and a method of fabricating an organic light emitting diode display using the same. More particularly, the present invention relates to a donor substrate having a structure capable of preventing or minimizing device substrate patterning defects due to unsuccessful layer transfer.
2. Description of the Related Art
Generally, an organic light emitting diode (OLED) display refers to a flat panel display having an anode electrode, a cathode electrode, and a plurality of organic layers interposed between the anode and cathode electrodes. The organic layers may include an emission layer, a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer. The material employed in the emission layer may determine the type of the OLED display, i.e., a polymer OLED display or a low molecular weight OLED display. The processing of the emission layer may determine the functionality of the OLED display, e.g., patterning of the emission layer may facilitate implementation of a full-color organic light emitting diode display.
Conventional patterning of the OLED display may be done by a fine metal mask, ink-jet printing, laser induced thermal imaging (“LITI”), and so forth. The LITI method, for example, may facilitate fine patterning of the OLED display and provide dry processing thereof, as opposed to wet processing, e.g., ink-jet printing. The conventional LITI method for forming a patterned emission layer of an OLED display may require forming a donor substrate having a base film, a light-to-heat conversion layer, and a transfer layer formed of an organic material, so that the transfer layer may be transferred from the donor substrate into a device substrate by using at least one light source, e.g., a laser.
More specifically, light may be emitted from the light source into a predetermined portion of the light-to-heat conversion layer of the donor substrate and converted therein into heat energy. Next, the heat energy may modify, an adhesive in the predetermined portion of the light-to-heat conversion layer, i.e., a portion radiated with the light source, so that the transfer layer may separate from the predetermined portion of the light-to-heat conversion layer and attach to the device substrate. Accordingly, one portion of the transfer layer may be attached to the device substrate, while another portion of the transfer layer may remain attached to the light-to-heat conversion layer. Therefore, a successful transfer of the transfer layer may depend on adhesion and cohesion properties of the materials employed, e.g., adhesion between the light-to-heat conversion layer of the donor substrate and the transfer layer, cohesion within the transfer layer, and adhesion between the transfer layer and the device substrate.
For example, if the adhesion between the light-to-heat conversion layer and the transfer layer is weak, the transfer layer may too easily separate from the light-to-heat conversion layer, i.e., a portion of the transfer layer intended to remain attached to the light-to-heat conversion layer may separate therefrom as well and, thereby, cause defects in the OLED display. The defect occurs more often, especially when the transfer layer is formed of low molecular weight materials exhibiting insufficient internal cohesion. On the other hand, if the adhesion between the transfer layer and the device substrate is too strong, the transfer layer may not be transferred or be torn during transfer.
Accordingly, there exists a need for a donor substrate capable of transferring a transfer layer onto a device substrate with an improved efficiency.